I recently acquired an old ebike battery. I have a small solar panel I currently use to charge some old lead acid batteries. While it functions fine for what I need, I’m considering transitioning over to the rechargeable lithium cells from the ebike battery. I find lots of cheap stuff on ebay for balancing and even BMS charging, but there’s not a lot of info on what sort of input voltage range. I know with my existing charge setup, the input voltage to the charge controller gets up toward 18V when its really sunny out. Also, I would like to set the charge voltage closer to 4.0V, rather than 4.2V. The cells in this pack are FST 18650-2500mAh.
Thats what i meant, it´s kinda doing “mppt”, the charge controller is not actively searching for the best working point, but it is keeping the voltage of the solar panel at its optimal operating point. In this case 18 Volts, so maybe it is better referred to as mpp not mppt.
Besides this still is a much better option than pwm charge controllers.
Thanks for the replies! I’ve come to realize also that I’ll need a seperate BMS. Do the cheap ones, or any for that matter, require the voltage into the BMS to be 12.6V? I’ve read that is the input voltage to them for the most part. That’s what made me think I needed another piece to regulate the cell stack voltage. I’m think of getting this solar charge controller, pretty inexpensive and good reviews. It also appears to have a voltage set function for Li Ion, which would be nice. Would rather charge to around 4V instead of 4.2 all the time.
So I am finally getting back to this project. I’m asking for some Christmas gifts to help me along.
Charger is this: [Newpowa 10A solar charge controller](“10A version Amazon.com”)
Balancer is this: [3s - 4s cell balancer](“3s-4s version Amazon.com”)
The battery has 13 rows of 4 cells in parallel, total of 52 cells. One of the 4P rows is down at 1.5V. That one won’t be used. I’m wondering if there’s an advantage to 3s or 4s. The manufacturer of the controller says in the lithium mode the charge voltage can be adjusted between 11.8 and 16.0 V in 0.1 V steps. So either would work. I’m leaning toward 3s, as it work well with cutting the connections and leaving most intact to create the battery (3s-4P, or actually 16P).
As I’m preparing for the electronics that will support the battery charging, I’m realizing that they also can support the battery build. the balancer can be used to balance the cells in a given position in each pack prior to connecting the packs in parallel. This will minimize any risk of damage when either two 20Ahr “cells” are connected to two other 20Ahr cells, or the 30Ahr cell is connected to the final 10Ahr cell. These cells I’m referencing, as noted above, are four 2.5Ahr cells in parallel. There’s a lot of charge that can move around, and I’ve been manually sort of balancing the cells just by charging them, but the final equilization can be accomplished via the balancer which as the capability of handling 4 cells.
Job is done. Based on the cells marking, I have a 3s 16p battery with 40Ahr capacity. It is powering a light by the front door that currently is drawing about 40mA, but I’ll likely adjust that up a bit. The stock LED draws about 200mA, but I find that running it lower provides a nicer illumination.